U.S. Pat. No. 5,759,271 (=EP 0 779 105 A1) shows a coating powder spray gun of this kind. It comprises a gun housing fitted with a tubular powder feed duct, a high-voltage chamber and further chambers all issuing openly from a rear end face of the gun housing. This document however remains silent whether the chambers are open or closed in the front end face of the gun housing. Gun housings of this kind known in practice are open at the front and at the rear. Practical designs most of the time call for a current limiting resistor between the high-voltage side of the high-voltage generator and the electrical contact in order to limit the high-voltage electrode's short-circuit current. The known powder spray gun may be affixed to a robot arm or on a support or another displaceable or immobile device.
A spray gun of a similar kind is known from U.S. Pat. No. 4,993,645 and includes a grip for manual handling.
A coating-powder spray gun used as a manual gun or as a machine-mounted gun is known from the U.S. Pat. No. 4,196,465. This document furthermore discloses details regarding a high-voltage generator received within the gun. Such a generator moreover may be configured outside the gun. Typically such a generator includes an oscillator converting a low input voltage into a low AC voltage, also a transformer connected to the AC output to transform up the said AC voltage and a cascade circuit containing a rectifier and capacitors or similar components to further raise the electrical voltage and to convert it into a high DC voltage for instance in the range from 2,000 to 170,000 v to be applied to one or more electrodes of said gun to electrostatically charge the coating powder.
The coating powder contains not only large powder particles, but also micro powder particles. The latter tend to penetrating the chambers at the front end face of the gun housing. As a result leakage currents, shorts and arcing from the high-voltage paths to the other components at lower potentials, for instance at ground, may occur, especially when the coating powder is electrically conducting or contains conducting components.